A Study of Atezolizumab Plus Carboplatin and Etoposide With or Without Tiragolumab in Patients With Untreated Extensive-Stage Small Cell Lung Cancer

This study will evaluate the efficacy of tiragolumab plus atezolizumab and carboplatin and etoposide (CE) compared with placebo plus atezolizumab and CE in participants with chemotherapy-naive extensive-stage small cell lung cancer (ES-SCLC). Eligible participants will be stratified by Eastern Cooperative Oncology Group (ECOG) Performance Status (0 vs. 1), LDH (\ ULN), and presence or history of brain metastasis (yes vs. no) and randomly assigned in a 1:1 ratio to receive one of the following treatment regimens during induction phase: * Arm A: Tiragolumab plus atezolizumab plus CE * Arm B: Placebo plus atezolizumab plus CE Following the induction phase, participants will continue maintenance therapy with either atezolizumab plus tiragolumab (Arm A) or atezolizumab plus placebo (Arm B).